JP2003059322A - Flat light source illuminating object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat light source, especially a backlight for a liquid crystal display device, with a simple structure, minimizing the light loss in a liquid crystal panel. SOLUTION: This flat light source illuminating an object has a light source; a light guide plate leading the thereinto from the end face opposite to the light source and diffusing the light, and reflecting the light on a reflection face to project the reflected light to the outside; and a prism sheet transmitting the reflected light and projecting the transmitted light as projection light in the normal direction to the object. A vertical angle of each microprism of the prism sheet is <=40 deg., and the microprisms are disposed face up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source, and a light guide plate which introduces light from an end surface facing the light source into the inside and diffuses the light, reflects the light at a reflecting surface and projects the reflected light to the outside. The present invention relates to a planar light source having a prism sheet that transmits this reflected light and projects it as projection light in the normal direction to irradiate an object to be illuminated. Particularly, in such a planar light source, the structure is simplified. In addition, the present invention relates to a planar light source that illuminates an illuminated object that is intended to illuminate the illuminated object more brightly by increasing the amount of light that illuminates the illuminated object.

[0002]

2. Description of the Related Art A planar light source used as a front light or a back light of a liquid crystal display device is already known. A planar light source used as a front light or a back light of this liquid crystal display device introduces light from a light source and an end surface facing the light source into the inside to diffuse the light, and reflects the light at a reflecting surface to reflect the reflected light. It is configured to have a light guide plate that projects to the outside, and a prism sheet that transmits the reflected light and projects it as projection light in the normal direction to irradiate a liquid crystal panel that is an illuminated object.

In a normal front light or backlight, a commercially available light guide plate or prism sheet is often used in combination, and the light guide plate and prism sheet are not always the optimum combination. No
In addition to having a more complicated structure than necessary, the light projected from the LED, which is a light source, is often not used to the maximum extent, and the amount of light that illuminates an illuminated object such as a liquid crystal panel with a planar light source is Often, it is only a part of the light projected from the light source LED.

The present invention and the prior art will be described below by taking a backlight of a liquid crystal display device as an example. FIG. 5 is a sectional view schematically showing an outline of a backlight of a conventional liquid crystal display device. As shown in FIG. 5, in a backlight 20 of a conventional liquid crystal display device, light projected from a light source 21, such as an LED (light emitting diode), has an end face 22 a of a light guide plate 22 arranged to face the light source 21. Introduced internally from
The light that is repeatedly reflected and diffused inside the light guide plate 22 and is reflected by the reflection surface 22b on the lower surface of the light guide plate 22 and directed upward is projected from the upper surface 22c of the light guide plate 22 to the outside.

The light projected from the light guide plate 22 to the outside is diffused by the diffusion sheet 23 and becomes light directed upward, and further, two prism sheets 24 and 25 in which the directions of the prisms are arranged orthogonal to each other. The light is refracted by and becomes a light toward a liquid crystal panel (not shown), and is projected from the upper surface of the prism sheet 25 on the upper side as illumination light onto an illuminated object (a liquid crystal panel not shown). The reflection sheet 26 arranged below the light guide plate 22 is for reflecting the light leaked from the lower surface of the light guide plate 22 and returning it to the light guide plate 22 again.

FIG. 6 is an explanatory view schematically showing the locus of light incident on the inside of the light guide plate. Light from the light source 21 that has entered the inside from the end surface 22a of the light guide plate 22 is reflected by the reflection surface 22b on the lower surface of the light guide plate 22 toward the upper side and refracted by the upper surface 22c, as shown by a ray A in FIG. And is projected in a direction inclined by an angle θ with respect to a normal line perpendicular to the upper surface 22c of the light guide plate 22. Then, the light projected from the upper surface 22c of the light guide plate 22 is orthogonal to each other of the prism sheets 24 and 25 arranged close to the light guide plate 22 and upwardly arranged micro prisms 24a and 25a (FIG. 4).
The light is refracted by the reference sheet) and is projected as illumination light from the upper surfaces of the prism sheets 24 and 25 toward a liquid crystal panel (not shown) which is an object to be illuminated.

Here, the light beam B in FIG.
2 is reflected by the upper surface 22c of the second light guide plate 22, then reflected again by the reflecting surface 22b of the lower surface of the light guide plate 22 toward the upper side, refracted by the upper surface 22c, and projected from the upper surface 22c of the light guide plate 22. An example of light that is repeatedly reflected between the upper surface 22c and the lower reflection surface 22b of the light guide plate 22 and diffused inside the light guide plate 22 is shown. Then, in this embodiment, the reflecting surface 2 of the stepped prism formed on the lower surface of the light guide plate 22.
Since 2b is inclined, the angle of the reflected light becomes closer to vertical every time it is reflected, and the light finally becomes the light projected from the upper surface 22c and is projected upward from the upper surface 22c. .

The angle θ of the light projected from the upper surface 22c of the light guide plate 22 toward the prism sheets 24 and 25 with respect to the normal line N is about 60 ° when the conventional light guide plate 22 is used. ˜80 ° and FIG.
The micro-prisms 24a and 25a of the prism sheets 24 and 25 shown in an enlarged view on the upper side of FIG. 1 have an apex angle of 90 °. In both cases, the micro-prisms 24a and 25a are arranged on the upper side. It was used by stacking two sheets in a direction orthogonal to each other.

In FIG. 7, in order to reduce the number of diffusing sheets and prism sheets and simplify the structure of the prior art, only one prism sheet 24 having a 90 ° apex angle of the microprisms is used for diffusing. It is the figure which simulated the locus | trajectory of the light which injected into the light guide plate 22 by the computer, when arrange | positioning except the sheet | seat 23 and the 2nd prism sheet 25. When the locus of the light incident on the light guide plate 22 of the backlight of this configuration is simulated by a computer and drawn, as shown in FIG. 7, the light in the direction inclined largely to the right from the normal line perpendicular to the upper surface of the prism sheet 24. It has become clear that the image is projected on the liquid crystal panel 27 as.

Here, the light that passes through the liquid crystal panel 27 as the illumination light becomes a component in the normal direction of the light projected from the prism sheet 24 onto the liquid crystal panel 27. Therefore, from the result of this simulation, the diffusion sheet 23 is obtained. And the second prism sheet 25 except for the micro prism 24a
When the apex angle of is 90 °, the projection angle of the light projected from the prism sheet 24 is 35 ° from the normal line.
Since the light is projected as a light inclined by about 40 °, the light loss in the liquid crystal panel 27 is large, which is not suitable for practical use.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves these problems of the prior art and simplifies the structure of the prism sheet and the diffusion sheet, and allows the prism sheet to enter the light guide plate and be reflected by the reflecting surface of the lower surface. It is an object of the present invention to provide a planar light source for illuminating an object to be illuminated, which is configured so that light transmitted through a sheet is projected substantially parallel to a normal line, and more specifically, is incident on a light guide plate. The light reflected by the lower reflection surface and transmitted through the prism sheet is projected substantially parallel to the normal line to provide a simplified planar light source, that is, a backlight of a liquid crystal display device. It is intended.

[0012]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art as described above, and introduces light from the light source and the end surface facing the light source into the inside, diffuses and reflects the light. A planar light source having a light guide plate that reflects light on a surface and projects reflected light to the outside, and a prism sheet that transmits the reflected light and projects it as projection light in a normal direction to illuminate an illuminated object This can be achieved by a planar light source for illuminating an object to be illuminated, characterized in that the apex angle of the micro prism of the prism sheet is 40 ° or less and the micro prism is arranged upward.

Here, it is preferable that the apex angle of the micro prism of the prism sheet is 30 ° to 25 °, the object to be illuminated is a liquid crystal panel, and a planar light source illuminates the liquid crystal panel. It is desirable that the backlight be used.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below with reference to the drawings illustrating an embodiment. FIG. 1 is a sectional view schematically showing an embodiment of a planar light source for illuminating an object to be illuminated according to the present invention, particularly a backlight of a liquid crystal display device. Here, the backlight 1 of the liquid crystal display device of the present invention is an LED.
The light guide plate 3 has a light source 2 formed of (light emitting diode) and the like, and the prism sheet 4 approaches the upper surface of the light guide plate 3 and
The reflector 5 is arranged close to the lower surface, and the diffusion sheet is not used.

Then, similarly to the backlight of the conventional liquid crystal display device, the light projected from the light source 2 such as an LED (light emitting diode) is emitted from the end surface 3a of the light guide plate 3 arranged so as to face the light source 2. Just like the light guide plate 22 that is introduced inside and described as the prior art in FIG. 6, total reflection is repeated between the upper surface 3c and the lower reflection surface 3b of the light guide plate 3 and diffused inside the light guide plate 3. At the same time, the light reflected by the reflection surface 3b on the lower surface of the light guide plate 3 and having a more nearly vertical angle is refracted and projected from the light guide plate 3 to the outside, and refracted again by the microprisms 4a of the prism sheet 4 and the liquid crystal It is projected as illumination light toward a panel (not shown). In addition, the reflection sheet 5 arranged below the light guide plate 3
Is also for reflecting the light leaked from the lower surface of the light guide plate 3 and returning it to the light guide plate 3 again.

Here, in the planar light source for illuminating the object to be illuminated of the present invention, the apex angle of the microprisms 4a of the prism sheet 4 is formed to be 40 ° or less as shown in an enlarged view on the upper side of FIG. , The microprisms 4a are arranged so as to face upward. Then, by forming the apex angle of the micro prism 4a in this manner, as shown in FIG.
As shown in, the illumination light projected from the prism sheet 4 onto the liquid crystal panel 6 which is the object to be illuminated can be light that is substantially perpendicular to the upper surface of the prism sheet 4.

FIGS. 2 to 4 are diagrams in which the locus of light incident on the light guide plate 3 is simulated by a computer when the apex angles of the microprisms are 40 °, 30 ° and 25 °. As shown in the drawing, the illumination light projected from the prism sheet 4 onto the liquid crystal panel 6 which is the object to be illuminated is inclined to the right in the embodiment of FIG. 2 in which the apex angle of the micro prism is 40 °, The apex angle of the prism is 30
In the embodiment of FIG. 3 which is 0 °, the light is slightly inclined to the right, and in the embodiment of FIG. 4 in which the apex angle of the microprism is 25 °, the light is almost perpendicular to the prism sheet 4. As is apparent from the figure, this inclination angle is about 15 ° at the maximum when the apex angle of the microprism is 40 °,
The loss of light that passes through the liquid crystal panel 6 as illumination light can be significantly reduced.

Further, according to the result of this simulation, it is apparent that the optimum apex angle of the micro prism is in the vicinity of 25 °. However, since this apex angle becomes thinner and sharper as the angle becomes smaller, it becomes difficult to form a large number of accurate shapes. In the present invention, it is desirable that the apex angle of the microprism is 40 ° or less, preferably 30 ° to 25 °, whereby the loss of light passing through the liquid crystal panel 6 as illumination light is substantially reduced. It can be reduced to a level that can be ignored.

As described above, the planar light source for illuminating the object to be illuminated according to the present invention, particularly the planar light source used as the backlight of the liquid crystal display device shown in the embodiment, is a micro prism sheet. The apex angle of the prism is 40 ° or less, preferably 30 ° to 25 °, and the structure is greatly simplified, such that only one prism sheet is arranged upward and the diffusion sheet is eliminated. It shows a basic configuration that enables the present invention, the present invention is not limited to the configuration described in the embodiments described above, within the scope not departing from the gist of the present invention Of course, various changes and improvements can be made.

[0020]

The surface light source for illuminating the object to be illuminated of the present invention,
In particular, in the planar light source that serves as the backlight of the liquid crystal display device as the embodiment, as described above, the apex angle of the microprisms of the prism sheet is 40 ° or less, preferably 3 °.
By setting the angle to 0 ° to 25 °, it was possible to use only one prism sheet with the microprisms facing upward, and one prism sheet and the diffusion sheet were not required as compared with the prior art. It is a thing. As a result, it has a great effect on cost reduction and ease of assembly, and the number of constituent parts can be greatly reduced to improve the product yield.

Further, by setting the apex angle of the micro-prism of the prism sheet to 40 ° or less, preferably 30 ° to 25 °, the loss of light passing through the liquid crystal panel as illumination light can be substantially ignored. Therefore, it is possible to provide a backlight for a liquid crystal display device in which the loss of light in the liquid crystal panel is minimized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an embodiment of a planar light source for illuminating an object to be illuminated of the present invention, particularly a backlight of a liquid crystal display device.

FIG. 2 is a diagram in which a locus of light incident on the light guide plate 3 is simulated and drawn by a computer when the apex angle of the micro prism is 40 °.

FIG. 3 is a diagram in which the locus of light incident on the light guide plate 3 is simulated and drawn by a computer when the apex angle of the micro prism is 30 °.

FIG. 4 is a diagram obtained by simulating with a computer the trajectory of light incident on the light guide plate 3 when the apex angle of the micro prism is 25 °.

FIG. 5 is a schematic cross-sectional view of a backlight of a conventional liquid crystal display device.

FIG. 6 is an explanatory diagram schematically showing the locus of light incident on the inside of the light guide plate.

FIG. 7 shows a vertical angle of 9 in order to simplify the configuration of the prior art.
It is the figure which simulated the locus | trajectory of the light which injected into the light-guide plate with a computer, when only one 0-degree prism sheet is used.

[Explanation of symbols]

1 Backlight of liquid crystal display 2 light sources 3 Light guide plate 3a end face 3b Reflective surface 3c upper surface 4 prism sheet 4a Micro prism 5 Reflective sheet 6 LCD panel

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Claims (3)

[Claims] 1. A light source, a light guide plate for introducing and diffusing light from an end surface facing the light source, reflecting the light on a reflecting surface and projecting the reflected light to the outside, and transmitting the reflected light. And a prism sheet for illuminating an object to be illuminated by projecting light as projection light in a normal direction, and the apex angle of the microprisms of the prism sheet is 40 °.
A planar light source for illuminating an object to be illuminated, which is characterized in that the microprism is arranged upward. 2. The planar light source for illuminating an object to be illuminated according to claim 1, wherein an apex angle of the micro-prisms of the prism sheet is 30 ° to 25 °. 3. The surface illuminating the illuminated object according to claim 1, wherein the illuminated object is a liquid crystal panel, and the planar light source is a backlight for illuminating the liquid crystal panel. light source.